Conventionally lane departure prevention devices are known to recognize a lane of a vehicle based on a photographed image of a driving environment in front of the vehicle using a camera or the like, estimate a position of the vehicle after a predetermined time from the recognition timing at control intervals, and when deviation of the vehicle from the recognized lane is expected, activate a steering actuator and a brake actuator to support deviation avoidance.
When this lane departure prevention device determines that the vehicle will depart from the lane and then detects a turn signal operation, the lane departure prevention device determines that the deviation is due to an intentional operation by the driver (e.g., lane change), and limits a deviation avoidance operation. In some travelling situations, a driver may change the lane intentionally without operating a turn signal. Therefore conventionally is known a technique to determine the operational intention of the driver on the basis of the output from a steering torque sensor detecting a steering torque by the driver as a signal other than the turn signal operation, to limit the deviation avoidance operation.
For instance, Patent Document 1 and Patent Document 2 disclose these conventional techniques.    Patent Document 1: JP Patent No. 3631825    Patent Document 2: JP Patent Application Publication No. 2008-290679 A